This invention relates to a current mirror circuit, and more particularly to a current mirror circuit which is used at an output stage of a multiplier or the like.
A current mirror circuit has been used at an output stage of a multiplier or the like for converting output currents of a differential amplifier to a single-ended output current. As disclosed in the "BIPOLAR AND MOS ANALOG INTEGRATED CIRCUIT DESIGN" by Alan B. Grebene, published from John Wiley & Sons, Inc. pp176-180, a conventional current mirror circuit has two transistors whose base electrodes are connected to each other, and two resistors having the same resistance and connected to emitter electrodes of the respective transistors. The current mirror accuracy depends on the resistance and becomes higher as resistance increases. It is preferable for the resistor to have a higher resistance.
In practical use, the transistors in such current mirror circuits are implemented as an integrated circuit. However, where the transistors in the integrated circuit have a lower break-down voltage, a power source of higher voltage cannot be used. When a lower-voltage power source (for example, .+-.5V), an increase in resistance causes a voltage drop by the resistor, resulting in a saturation of the transistor. In other words, it is impossible in practice to increase the resistance. As a result, current mirror accuracy can not be improved.